Current electronic systems, such as OSCs, require complex technologies which make it problematic to optimize their optical performance and electronic performance.
One of the main optimization routes consists in using, at the anode of the photovoltaic system, a conducting polymer such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), the latter being inserted between a tin-doped indium oxide (ITO) electrode and a photosensitive active layer (Crispin et al., Journal of Polymer Science: Part B: Polymer Physics, Vol. 41, 2561-2583 (2003)). The substrates coated with PEDOT:PSS are optically anisotropic and do not absorb very much in the visible region; the conductivity of the substrates coated with PEDOT:PSS prepared by means of commercial solutions is generally between 1 and 50 S·cm−1.
Devices based on PEDOT:PSS today still form the subject of numerous studies (Groenendaal et al., Adv. Mater., 2000, 12, No. 7) relating to:                the improvement in the photosensitive active layer by the use of novel absorbent materials, by the charge network structuring or also by the improvement in the transportation of the charges, and        the improvement in the interfaces by virtue of a better quality of the contacts or a collecting of the charges.        
Thus, the anode interfacial layers used in electronic devices should exhibit:                good electronic properties and more particularly a high conductivity, and also a suitable work function which makes it possible to optimize the energy barrier at the interface between the ITO electrode and the photosensitive active layer, facilitating the collection of the positives charges,        good optical properties which are characterized by a minimum absorption, and        good stability and an ease of forming which makes possible the formation of homogeneous and continuous films.        
Work function is understood to mean the minimum energy, measured in electron volts (eV), necessary in order to extract an electron from the Fermi level of a metal to a point located at infinity outside the metal. The photoelectric effect consists of release of an electron when a photon having an energy greater than the work function arrives on the metal. The difference between the energy of the incident photon and the work function is supplied to the electron in the form of kinetic energy. Thus, the photoelectric work function is calculated according to the formula:φ=h·f0 where h is Planck's constant and f0 is the minimum frequency of a photon starting from which photoelectric emission occurs.
The work function of the electrodes plays a crucial role in the field of plastic electronics because it influences the distribution of the internal electric field and the height of the energy barrier between the electrode and the photosensitive active layer of the device. This barrier greatly influences the injection of the charge carriers, in particular in the case of organic light-emitting diodes (OLEDs), or, on the contrary, dominates the collection of the charges of the active layer towards the electrode, such as, for example, in the case of OSCs. In order to facilitate the transportation of the holes, materials exhibiting high work functions are preferred as anode.
Currently, the most commonly used devices are devices based on PEDOT:PSS. However, when it is used as interfacial layer on ITO electrodes, PEDOT:PSS has to be applied in the form of a thin film having a thickness of less than approximately one hundred nanometers, in order to guarantee a high optical transmission; the PEDOT:PSS film exhibits, in this case, a low conductivity. Surface defects and holes can also appear at the surface of the PEDOT:PSS film when the polymer layers applied are excessively thin. On the other hand, when it is applied as a thicker layer (between 150 and 200 nm in thickness), i.e. in order to achieve higher conductivities which make possible lateral transport of the photocurrent, a loss at the level of the optical transmission coefficient is then observed.
Systems based on PEDOT:PSS also have other disadvantages:                the interface between the PEDOT:PSS films and the ITO-based electrodes is unstable, the indium atoms diffusing into the polymer layer and detrimentally affecting its performance,        the electric contact between the PEDOT:PSS films and the ITO-based electrodes is slight, the polymer layer not accessing numerous electronically active sites of the surface of the ITO electrode, which increases the series resistances and greatly decreases the collection of holes at the electrode,        the conductivity and the roughness of the PEDOT:PSS layers are dependent on the application conditions and in particular on the moisture content and on the annealing temperatures.        
Replacement routes for the use of conducting polymers at the anode interface have also been envisaged, such as, for example:                the use of monolayers (Campbell et al., Appl. Phys. Lett., 71 (24), 3528-3530; Kim et al., Appl. Phys. Lett., 92, 133307 (2008); Akkerman et al., Small, 2008, 4, No. 1, 100-104; Armstrong et al., Thin Solid Films, 445, 2003, 342-352), the latter generally being covalently bonded, by the chemical or electrochemical route, to the surface of the ITO electrode. However, these monolayers are not very thick (a few tens of angstroms) and result in unequal covering of the substrates which they functionalize, allowing roughnesses to remain and thus resulting in interfaces of mediocre quality,        the use of charge transfer complexes (Hanson et al., J. Am. Chem. Soc., Vol. 127, No. 28, 2005, 127, 10058-10062; Kahn et al., Appl. Phys. Lett., Vol. 79, No. 24, 4040-4042), the latter nevertheless exhibiting the disadvantage of having energy levels which are difficult to adjust.        